1. Field of Invention
The present invention relates to an electrostatic discharge protection apparatus. More particularly, the present invention relates to an electrostatic discharge protection apparatus for a circuit board.
2. Description of Related Art
Electronic devices, such as monitors, notebook computers, mobile telephones, are easily damaged by electrostatic discharge (ESD) that affects normal operations of these electronic devices. The transient voltage induced by electrostatic discharge is very large, and as the scale of integrated circuit elements is reduced, the threshold electrostatic voltage that may cause electrostatic discharge also becomes smaller. In practical operations, some high-speed electronic devices may be damaged when the magnitude of the electrostatic discharge is only 30 V.
Electrostatic discharge occurs because an electric field formed by charged objects ionizes neighborhoring gases to induce discharge. Both conductors and nonconductors can induce and accumulate electric charges. Generally, a material with low resistance easily dissipates electric charges, but a material with high resistance dissipates electric charges with difficulty. For this reason, nonconductors very easily accumulate electrostatic charges. Artificial polymers, like plastics, are able to gather and keep electrostatic charges for a long time due to their high resistance.
Electrostatic discharges include direct electrostatic discharges and indirect electrostatic discharges. The direct electrostatic discharges are further divided into contact discharge and air discharge according to their different discharging methods. The indirect electrostatic discharges are also further divided into horizontal coupling place (HCP) discharge and vertical coupling place (VCP) discharge.
Contact discharge is point discharge, such when as a screwdriver damages electronic devices, and mainly occurs in a joint of two metal pieces or a surface of one metal piece. Air discharge is human body discharge, such as when a finger damages electronic devices, and generally occurs on a nonconductive surface, like the case of an electronic device, or a surface that is often be touched by fingers, like a keyboard.
Manufacturers usually apply ESD tests to electronic devices to ensure their resistance to electrostatic discharge and ability to maintain stable work conditions. The environment of the ESD test is a temperature of: 15xc2x0 C.-35xc2x0 C., a relative humidity of: 30%-60% and an atmospheric pressure of: 68 Kpa (680 mbar)-106 Kpa (1060 mbar). The ESD test simulates electrostatic discharge to test whether electronic devices can effectively avoid electrostatic discharge under different discharge conditions.
FIG. 1 illustrates a schematic view of a circuit board, such as a mainboard 100, and in particular a view of a side without any chip of the mainboard 100. The mainboard 100 includes several screw holes, and screws fasten the mainboard 100 to something through the screw holes. Moreover, the mainboard 100 also comprises multiple input/output ports (I/O ports) 104 and slots 106.
The screws, the I/O ports 104 and the slot 106 all accumulate electric charges, and their ends are pointed. Charged objects easily discharge from their pointed end when they gather electric charges. The screws, the I/O ports 104 and the slot 106 therefore very easily discharge, and then damage the electronic element on the mainboard 100.
Generally, a circuit board includes several ground layers inside to dissipate the electric charges accumulated on its charged objects. Because of the trade-off with cost, sometimes the circuit board contains only 6 layers instead of the conventional 8 layers. The 6-layer circuit board has one less ground layer than the conventional 8-layer circuit board, so the electrostatic discharge protection ability of the 6-layer circuit board decreases substantially. Thus the slayer circuit board usually can""t pass the ESD test before it leaves the factory.
It is therefore an objective of the present invention to provide an electrostatic discharge protection apparatus for a circuit board, that satisfies this need to improve the electrostatic discharge protection ability of the circuit board.
In accordance with the foregoing and other objectives of the present invention, an electrostatic discharge protection apparatus for a circuit board is described. The electrostatic discharge protection apparatus for a circuit board is placed in the neighborhood of some pointed ends of the circuit board, such as screws, I/O ports or slots. The electric charges accumulated on the pointed ends therefore dissipate by jumping to the electrostatic discharge protection apparatus, and thus the electric charges accumulated are prevented from inducing discharge.
In one preferred embodiments of the present inventions, a nonconductive layer contacts a backside of a mainboard, and a conductive layer contacts the opposite side of the nonconductive layer.
The material of the nonconductive layer is insulating and plastic, for example, polyethylene terephthalate (PET) is appropriate as a material of the nonconductive layer. The material of the conductive layer is aluminum, copper, or other metal that is conductive and processed easily.
The conductive layer of the preferred embodiment further comprises a ground port. The conductive layer is coupled with a ground end by the ground port to enlarge the effective area of the conductive layer dissipating and containing the electric charges.
The nonconductive layer comprises several openings corresponding to the screw holes of the mainboard. Similarly, the conductive layer also comprises several openings corresponding to the screw holes of the mainboard.
Moreover, the apparatus of the invention comprises the same functional openings for other pointed ends on the mainboard 100, like I/O ports and the slots.
The area of the conductive layer can be used to modify the electrostatic discharge protection ability of the apparatus.
The nonconductive layer and the mainboard can be fixed together to avoid relative movement therebetween that would reduce the electrostatic discharge protection ability. The nonconductive layer and the conductive layer can do this as well. In this preferred embodiment, an adhesive element, like glue, is used to fix them.
In conclusion, the present invention improves the electrostatic discharge protection ability of the conventional circuit board, and is a cheap and simple apparatus for the circuit board. Utilizing the present invention on a circuit board allows the circuit board to pass an ESD test before it leaves the factory even as the circuit board structure shrinks from 8 layers to 6 layers. The cost of a 6-layer circuit board with this apparatus is only about a quarter of the cost of a slayer circuit board with 2 additional ground layers inside. Therefore, the apparatus of the present invention not only saves costs, but also helps the circuit board pass the ESD test.
It is to be understood that both the foregoing general description and the following detailed description are examples, and are intended to provide further explanation of the invention as claimed.